Synthesis and characterisation of carboxy amide-bonded pyridinium Gemini surfactants: influence of the nature of the spacer group and counterions on the aggregation behaviour

A series of novel dimeric pyridinium surfactants has been synthesised and the effects of a semi-flexible p-xylyl spacer and flexible, polyethylene glycol spacers have been studied. The nature of the spacer determines solubility and aggregation behaviour in two- and three-dimensional systems. Some of these insoluble compounds form two-dimensional, rigid-condensed structures at the air-water interface, while others form liquid-analogue monolayers. Whereas the latter compounds become soluble after exchange of the counterions, the former remain insoluble. The aggregation behaviour of Langmuir layers was, inter alia, investigated by Brewster angle microscopy. The micellisation behaviour of diluted aqueous solutions of soluble surfactants was primarily investigated by conductometric measurements and thermodynamic parameters of aggregation have been deduced with respect to the spacer length.